The undecatungstocobaltoindic heteropoly acid H-7[In(H2O)CoW11O39].14H(2)O was synthesized for the first time by the stepwise acidification and the stepwise addition of solutions of the component elements as well as the ion exchanging-cooling method. The optimal proportion of the component compounds and the pH of the synthesis reaction are given. The product was characterized by means of inductively coupled plasma (ICP), IR, UV, X-ray diffraction, and thermal analysis. The IR, UV and XRD indicate that H-7[In(H2O)CoW11O39].14H(2)O possesses the Kegginstructure. The results of AC impedance measurement show that its proton conductivity is 6.64 x 10(-3) S cm(-1) at room temperature (18 degrees C). (c) 2005 Elsevier B.V. All rights reserved.